Electrical generators generate electrical power to a greater extent at increasing speeds. Thus, vehicle alternating electrical generators or alternators do not generate anywhere near as much power at engine idle speed as at normal driving speeds. Use of a gear unit to increase the rotor speed of a conventional generator in order to generate more power at engine idle speed also provides a proportional increase in the rotor speed at normal driving speeds and can produce vibration and other problems.
One use for which it is particularly desirable to have an electrical generator that provides high output at low speeds is for a hermetically sealed vehicle air conditioning system wherein the input is electrical power as opposed to a belt and pulley driven compressor in accordance with conventional vehicle air conditioning systems. Electrically heated windshields are another use for which it is particularly desirable to have an electrical generator that provides high output at low speeds.